This invention relates to a method of making a pipe fitting and, more particularly, to a fitting having three or more legs arranged in any desired shape. It constitutes an improvement on U.S. Pat. No. 3,961,513 granted June 8, 1976.
Fittings of the type contemplated by the invention are used in a wide variety of fluid-conducting installations and, when the legs are curved, provide an extremely advantageous return bend connection for equipment using coils (either for heating or cooling).
Inasmuch as fittings (and the coils or other tubing to which they are attached) are of relatively small size -- generally ranging in outside diameters from 3/8 inches to 1/2 inches, with diameter to wall thickness ratios of about 5 to 30 -- it is important that the interior walls of the fittings be relatively smooth with the tubes having a fairly uniform inside diameter so as not to restrict fluid flow. Additionally, because these fittings are integrated into coil equipment and the like, as by brazing or other heat employing uniting operations, it is important that the fitting have high structural integrity so as to resist deformation which could result in resistance to fluid flow -- or even premature rupture, resulting in extensive and expensive repair.
The invention herein is specifically directed to the making of a pipe fitting having three or more legs arranged in any desired manner from an elongated tube wherein the legs have a length to diameter ratio of more than 3 and where the ratio of diameter to wall thickness of the fitting is in the range of about 5 to 30. It will be appreciated that the provision of such a fitting requires extensive shifting of metal and the invention in the above identified patent sought to achieve this through the provision of a thicker wall adjacent the closed end of the starting tube or capsule. Although the invention of the above identified patent provides fittings characterized by a high degree of integrity, it has not provided fittings wherein the wall thickness is substantially uniform throughout the various branches of the fitting, i.e., less than about 10% variation. In fact, in some instances, the variation in wall thickness in products made according to the above identified patent ranges as high as 200%. Although the thicknesses per se are relatively small -- of the order of 0.018-0.035 inches, the substantial variation does impede fluid flow and further makes difficult the union of the fitting into a piping system -- it is difficult to braze different thickness walls together because the thicker wall element takes longer to heat and provides a "heat sink" effect.
The problems of the prior art have been solved through the employment of a constant volume filler material during the deformation of the elongated tube and maintaining the filler material at constant volume throughout the deformation. Additionally, I have found it advantageous to position the leg-forming cavities intermediate the length of the tube particularly where the fitting has fairly long legs to avoid shear planes, flow faults, or buildup. With the constant volume filler material, metal from both ends of the tube flows or feeds into the legs -- thereby achieving a process akin to extrusion as contrasted to the "bulging" characteristic of the prior art procedures -- as in U.S. Pat. No. 3,681,960.
Other objects and advantages of the invention may be seen in details of the ensuing specification.